Solvent cement

ABSTRACT

The present invention describes novel solvent cements which are a combination of a solvent which is a 5- or 6-membered ring lactam and a cosolvent which is one or more lower alkanols and/or one or more lower alkyl esters of lower alkanoic acids and, optionally, includes a water-insoluble polymer such as PVC or ABS.

This is a division of application Ser. No. 822,861, filed Jan. 27, 1986.

BACKGROUND OF THE INVENTION

The glue and cement art is a mature technology. Many and varied gluesand cements have been described and much speculative disclosure has beenmade about such compositions. In spite of, or perhaps because of theabundance of information available about glues and cements, needs forimproved compositions continue to exist. It has become extremelydifficult to find the necessary information about suitable cements forspecific purposes.

The need for safer cements has become more apparent as industry and theconsumer have become more aware of the potential toxic liabilities ofvarious glue and cement solvents, but these cements must effectivelybond. In view of this need for increased safety, certain cements haveutilized cyclic 5- or 6-membered ring lactam solvents such asN-methyl-2-pyrrolidone.

U.S. Pat. No. 3,404,117 of Uffner describes an adhesive film-formingcomposition that, when in the dry state, is insoluble in either water ordry cleaning solvents. The adhesive comprises a blend of one of acertain class of fluorinated copolymers and a plasticizer in a solvent.Some of the solvents claimed are N-methyl-2-pyrrolidone and aliohaticalcohols.

G.B. Pat. No. 1,572,481 describes an " . . . adhesive containingpolyvinyl alcohol or ethylene/vinyl alcohol cpolymer, a crystallinesolvent for the polymer and a viscosity-reducing diluent." Theviscosity-reducing diluents include polyhydric alcohols.

U.S. Pat. No. 2,616,868 of Heisenberg and Kleine describes liquidcompositions for solutions of polymers and copolymers of vinyl chloridewhich are used to spin threads. In their description of the prior art,Heisenberg and Kleine point out that there are a series of lactones andlactams which, according to the literature, are " . . . suitable assolvents for polymers and copolymers of vinyl compounds."

Fogle, et al, U.S. Pat. No. 4,152,313, describe an adhesive compositionof " . . . vinyl acetate-ethylene emulsion and an admixture of tolueneand N-lower alkyl substituted pyrrolidone."

Still other adhesives for use in joining plastics, such as plastic pipesor the like, are known and generally comprised of polymers such aspoly(acrylonitrile-butadiene-styrene) (ABS) or poly(vinylchloride) (PVC)in a solvent or a blend of solvents such as methyl ethyl ketone, tolueneand/or tetrahydrofuran.

Still other adhesives for use in pipes or the like are known whichcomprise a suitable polymer such as ABS or PVC and a solvent mixtureconsisting only of lactones or lactams, and in particular, preferredlactams such as N-methyl-2-pyrrolidone (NMP). These formulations performwell in warm weather and at elevated temperatures, but their propertiesas bonding agents are less acceptable under low temperature conditions.

Generally, the requirements for solvent cements for use in the plasticindustry require that certain strength criteria are met and that thesolvents be suitable for use without causing undue user health problems.The standards for solvent cements for use in the United States arespecified in Bulletin ASTM D2564-80, published by the American Societyfor Testing Materials, 1916 Race Street, Philadelphia, PA. The ASTMSpecification for "Solvent Cements for Polyvinyl Chloride Plastic Pipeand Fittings" specifies that the solvent cement should have certainminimum resin content and meet certain minimum requirements forviscosity and strength. For example, the specified minimum resin contentfor cement for PVC pipe is 10% by weight of the solution and the lapshear strength when tested in accordance with the test proceduresrequires that the joint between two surfaces have a strength of at least250 psi after a 2 hour curing time, at least 500 psi after a 16 curingtime, and at least 900 psi after a 72 hour curing time.

Since, generally, these solvent cements are made from flammable liquids,the specification requires that the solvent should be kept away fromsources of ignition and, in addition, ventilation should be maintainednot only to minimize fire risk, but to minimize breathing of solventvapors. In addition, one should avoid direct contact of the solventcement with the user.

One of the preferred adhesive solvents is N-methyl-2-pyrrolidone. Whileit is flammable, it has a relatively high flashpoint of 204° F. and,according to the manufacturer, it has a low order of oral toxicity andonly produces mild topical effects. Because of these characteristics,N-methyl-2-pyrrolidone is one of the better or safer solents to use inthe solvent cements. However, when N-methyl-2-pyrrolidone alone is usedin combination with resins such as ABS or PVC as specified by the ASTMTesting Standards, the solvent adhesive may not pass the lap shearstrength requirements.

SUMMARY OF THE INVENTION

The present invention provides novel solvent cements which provide andcombine acceptable characteristics in their properties of flammability,safety to the user, environmental acceptability, and bonding strength.

The invention relates to cements comprising a combination of a solventwhich is a 5- or 6-membered ring lactam and a cosolvent which is one ormore lower alkanols and/or one or more lower alkyl esters of loweralkanoic acids and, optionally, include a water-insoluble polymer suchas poly(vinylchloride) or poly(acrylonitrile-butadiene-styrene).

The invention also relates to a method for forming a cemented juncturebetween surfaces of articles comprising primarily water-insolublepolymers such as PVC and/or ABS which comprises applying a cement of theinvention to at least one of the surfaces to be joined, mating thesurfaces to be joined, and allowing the juncture to form.

This invention also relates to the use of thixotropic, e.g.,viscosity-adjusting agents, in combination with the solvent adhesives ofthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In my solvent cement, I have found that although certain solvents whenused alone have insufficient adhesive properties to produce a solventadhesive of sufficient strength to meet the ASTM lapshear testrequirements, when combined and added to a polymer resin, thesecombinations produce a solvent adhesive which exceeds ASTM lapshearstrength requirements. More particularly, I have found that thecombinations of cyclic 5- or 6-membered ring lactams such asN-methyl-2-pyrrolidone and either lower alkanols such as methyl alcoholor lower alkyl esters of lower alkanoic acids such as ethyl acetate,alone or together with resins such as ABS or PVC, produce a solventcement which meets or exceeds the lapshear strength requirementsspecified in the ASTM Test Standards. This is particularly surprising inview of the fact that methyl alcohol or ethyl acetate alone or togetherwith ABC or PVC do not provide good solvent cements.

Suitable 5- or 6-membered ring lactams for use in the cements of thepresent invention include N-phenyl-2-pyrrolidone, 2-piperidone,2-pyrrolidone, N-ethyl-2-pyrrolidone, N-methyl-2-pyrrolidone, andequivalents thereof. N-Alkylated lactams, particularly N-methylatedlactams, are preferred. Presently preferred is N-methyl-2-pyrrolidonebecause of its ready availability and relatively low cost.

Suitable lower alkanols for use in the cements of the invention arepreferably alkanols of four carbon atoms or less such as methanol,ethanol, isopropanol and n-butanol. Methanol is presently preferredbecause of its ready availability and low cost.

Suitable lower alkyl esters of lower alkanoic acids are preferablyesters of lower alkanols as defined above and lower alkanoic acids ofone to four carbon atoms such as methyl acetate, ethyl acetate, ethylformate, ethyl propionate and the like. Ethyl acetate is presentlypreferred.

The polymer or polymer mixture dissolved in the solvent mixture to formthe cement of the invention may be any water-insoluble synthetic organicpolymer which is soluble in the solvents to provide an effective cement.Suitable polymers include PVC, ABS, polycarbonate, polystyrene,polyacrylates, cellulose acetate, polyacrylamide, polyamide, and thelike. Of these, PVC and ABS are of most interest due to their widespreaduse. The polymer or polymer mixture dissolved in the solvent mixture toform the cement of the invention may be polymer waste or freshlyprepared polymer. Generally, the polymer or polymers in a cement areidentical, or at least chemically similar, to the polymer(s) to becemented.

In general, I have found that if methyl alcohol is used, the alcoholmaximum percentage should not exceed 20% by weight or jelling occurs,and minimum percentage rate of alcohol should be approximately 3% byweight or more to provide a workable rangefor the adhesive when theresin content is about 12%. As the percentage of alcohol decreases inthe mixture, it is still usable; however, the lowering of the alcoholcontent has a diminishing effect on the effectiveness of bonding by thesolvent adhesive. It is presently preferred to use methanol-basedcements of about 78% NMP, 10% methanol, and 12% resin.

When ethyl acetate is used in the solvent adhesive, the workable rangeof ethyl acetate ranges from a maximum of 51% by weight of ethyl acetateto a minimum of approximately 3% of ethyl acetate when the resin contentof the cement is about 13%. As a general rule, the lesser the amount ofethyl acetate, the lesser the effectiveness of the strength of bondingby the solvent adhesive.

When the cements of the invention are a combination of NMP, ethylacetate and a resin such as PVC or ABS, it has been found that gellationof the cements, particularly upon aging, can occur when the percent ofresin is 10 to 15% and the amount of ethyl acetate significantly exceeds50%, for example, when it is 60% or more. When the resins are omittedfrom the formulations, amounts of ethyl acetate can easily be 75%, andamounts as high as 90% have been successfully used.

In general, the solvents such as methyl alcohol and ethyl acetate havebeen found to decrease cure time of the cement so that one can obtainhigher structural strengths at lower cure times.

In a further preferred embodiment of the invention small amounts of athixotropic agent, e.g., colloidal silica, which provides viscositycontrol, and optionally, a small amount of an inert metal salt are addedto the cement of the invention.

Suitable thixotropic agents are added in relatively small amounts, forexample, from about one to five percent by weight of the totalformulation. Preferably, they are added in amounts of two to threepercent. These agents have been found to be useful for viscosity controlin the cements of the invention, although they also increase thecomplexity and the cost of the cements and are, therefore, most usefulin specialized situations where the incremental cost differential isjustified by the improved properties.

It has been found that the cements of the present invention improve inquality, i.e., they provide improved bonding, as they age. By aging, Imean standing on the shelf before use.

In general, small amounts, i.e., generally less than five percent, ofinert diluents such as metal salts can be added to the cements of theinvention without deleterious effect. For example, from one to twopercent of sodium chloride was added to several formulations of theinvention and these cements had excellent bonding properties.

The following are typical examples of mixtures of the present invention.

EXAMPLE 1

Approximately 78.3% by weight of N-methyl-2-pyrrolidone was added to5.7% methyl alcohol with the balance being ABS resins. After mixture,the solvent cement was applied to test samples and cured in accordancewith the ASTM Standards and subjected to shear tests at 2 hour, 16 hour,and 72 hour intervals. Two samples of each were tested and all of thesamples exceeded the test requirements.

EXAMPLE 2

Example 1 was repeated except PVC resins were used and, again, all thetest results for the 2, 16, and 72 hour cure exceeded the ASTMStandards.

EXAMPLE 3

A batch of solvent adhesive was formed by mixing approximately 36% byweight of N-methyl-2-pyrrolidone with approximately 51% by weight ethylacetate and approximately 13% by weight ABS resin. The solvent cementwas applied to test samples and allowed to cure and was tested at 2, 16,and 72 hour intervals. Each of the samples exceeded the ASTM Standards.

EXAMPLE 4

The solvent adhesive of Example 3 was prepared except that PVC resinswere used in place of the ABS resins. The samples were, again, found toexceed the ASTM test requirements.

The following Table I is illustrative of the test results obtained withdifferent amounts of NMP and methyl alcohol (Me) on bonding of PVC toPVC. In order to meet ASTM lap shear requirements, the average (twosamples) bond strength at 2 hours should exceed 250 psi, at 16 hoursshould exceed 500 psi, and at 72 hours should exceed 900 psi.

                                      TABLE I                                     __________________________________________________________________________    Ex.                                                                              Composition        Avg. Lap Shear Strength                                                                    Test                                       No.                                                                              Solvents                                                                             Resin/Adjuvant                                                                            [PVC to PVC (psi)]                                                                         Hours                                      __________________________________________________________________________    5  78.3% NMP                                                                            12% PVC/2.9%                                                                              366          2                                             5.75% Me                                                                             Aerosil*, 1.2% NaCl                                                                       876          16                                                               1150         72                                         6  78.3% NMP                                                                            12% PVC/2.9%                                                                              341          2                                             5.75% Me                                                                             Aerosil, 1.2% NaCl                                                                        744          16                                                               966          72                                         7  74% NMP                                                                              11.2% PVC/2.7%                                                                            483          2                                             10.9% Me                                                                             Aerosil, 1.1% NaCl                                                                        792          16                                                               1016         72                                         8  76.1% NMP                                                                            11.5% PVC/2.8%                                                                            416          2                                             8.4% Me                                                                              Aerosil, 1.1% NaCl                                                                        804          16                                                               1000         72                                         9  71.8% NMP                                                                            10.9% PVC/2.6%                                                                            525          2                                             13.6% Me                                                                             Aerosil, 1.1% NaCl                                                                        684          16                                                               1075         72                                         10 71% NMP                                                                              11% PVC/2% Aerosil                                                                        408          2                                             15% Me 1% NaCl     852          16                                         11 74.6% NMP                                                                            11.3% PVC   322          2                                             14.1% Me                                                                   12 81.6% NMP                                                                            12.4% PVC   314          2                                             6% Me                                                                      __________________________________________________________________________     *Aerosil is colloidal silica available from Degussa                      

Table II illustrates the test results for average (two samples) lapshear strngth (given in psi) obtained with varying amounts of ethylacetate (EA) and added resins in combination with NMP on bonding of ABSto ABS, ABS to PVC, and PVC to PVC.

                                      TABLE II                                    __________________________________________________________________________    Ex.                                                                              Composition       Average Lap Shear Strength                               No.                                                                              Solvents                                                                             Resins                                                                              Adjuvant                                                                           ABS to ABS                                                                           ABS to PVC                                                                           PVC to PVC                                                                           Hours                               __________________________________________________________________________    13 65.5% NMP                                                                            2.1% ABS                                                                            2.2% --     508    558    2                                      21.8% EA                                                                             8.4% PVC                                                                            Aerosil                                                                            --     789    851    16                                  14 71.4% NMP                                                                            2.1% ABS                                                                            none --     458    516    2                                      17.8% EA                                                                             8.6% PVC                                                            15 36% NMP                                                                              2.1% ABS                                                                            2.6% --     462    558    2                                      51% EA 8.3% PVC                                                                            Aerosil                                                                            850    1030   1100   16                                                       --     1150   1436   72                                  16 65.5% NMP                                                                            2.1% ABS                                                                            2.1% --     450    500    2                                      21.8% EA                                                                             8.4% PVC                                                                            Aerosil                                                                            --     1119   1256   72                                  17 36% NMP                                                                              2.1% ABS                                                                            2.6% --     458    465    2                                      51% EA 8.35% PVC                                                                           Aerosil                                                                            --     870    1024   72                                  18 36% NMP                                                                              4.9% ABS                                                                            none 250    250    275    2                                      49% EA 9.8% PVC                                                            19 40% NMP                                                                              3% ABS                                                                              none 362    312    425    2                                      48% EA 9% PVC                                                              20 43.4% NMP                                                                            2.2% ABS                                                                            none 312    325    350    2                                      43.4% EA                                                                             11% PVC                                                             21 40% NMP                                                                              12% PVC                                                                             none 325    275    412    2                                      48% EA                                                                     __________________________________________________________________________

EXAMPLE 22

In order to evaluate the necessity for dissolved resin in the cements ofthe invention, a cement comprising 25% NMP and 75% EA was used to bondABS to PVC and PVC to PVC, and the average (two samples) ASTM lap shearstrength for each formulation was measured at two hours. The resultsshowed 300 psi for ABS to PVC and 462 psi for PVC to PVC. Both resultsare well above the ASTM Standards.

EXAMPLE 23

A cement comprising 10% NMP and 90% EA was used to bond ABS to ABS, ABSto PVC, and PVC to PVC, and the average (two samples) ASTM lap shearstrength for each formulation was measured at two hours. The resultsshowed 232 psi for ABS to ABS, 265 psi for ABS to PVC, and 288 psi forPVC to PVC. The ASTM Standard is not met for bonding of ABS to ABS,indicating that the use of this formulation would be limited to bondingof ABS to PVC and PVC to PVC.

What is claimed is:
 1. A solvent cement for joining insoluble waterpolymers wherein the solvent cement exceeds the standard specified inASTM Bulletin D-2564-80, consisting of a solution of a solvent of ethylacetate and N-methyl-2-pyrrolidone and wherein the ethyl acetate rangesfrom a minimum of approximately 3% to a maximum of about 90%, with thebalance N-methyl-2-pyrrolidone.